1. Field of the Invention
The present invention relates to an internal teeth oscillating inner gearing planetary gear system.
2. Description of the Related Art
Conventional inner gearing planetary gear systems are found widely in various areas where reducers are used, owing to the advantages of large torque transmission capability and large reduction ratios being obtainable.
Among such devices, internal teeth oscillating-type inner gearing planetary gear systems are known wherein rotation of an input shaft is reduced and delivered from an output member through oscillatingly rotating internal teeth oscillating bodies around an external gear, the internal teeth oscillating body having a slight difference in the number of teeth with the external gear (for example, Japanese Patent No. 2607937).
An example of the same gear system will now be explained using FIGS. 4 and 5.
In the drawings, a casing 1 has a first support block 1A and a second support block 1B joined together by insertion of an engaging member such as bolts or pins (not shown) into engaging holes 2. A pinion 6 is disposed on the end of an input shaft 5, and the pinion 6 meshes with a plurality of eccentric shaft gears (eccentric shaft driving gear or transmitting gear) 7 disposed at equal angles around the input shaft 5.
In the casing 1, three eccentric shafts 10 are disposed circumferentially at equal-angled intervals (120 degree intervals). The eccentric shafts 10 are supported to be freely rotatable at both axial ends by bearings 8 and 9, and have eccentric bodies 10A and 10B which are in an axially midway portion thereof. The eccentric shaft gears 7 are joined to respective end portions of the eccentric shafts 10. The eccentric shaft gears 7 are rotated by the rotation of the input shaft 5, to rotate each of the eccentric shafts 10.
The eccentric shafts 10 pass through eccentric holes 11A and 11B of two internal teeth oscillating bodies 12A and 12B contained in the casing 1, respectively. Rollers 14A and 14B are disposed between outer circumferences of the two eccentric bodies 10A and 10B adjoined in the axial direction of the eccentric shafts 10 and inner circumferences of the through eccentric holes 11A and 11B of the internal teeth oscillating bodies 12A and 12B, respectively.
An external gear 21 integrated with the end of an output shaft 20 is disposed at the central portion inside the casing 1. Internal teeth 13 formed from pins of the internal teeth oscillating bodies 12A and 12B mesh with external teeth 23 of the external gear 21. A difference in the number of teeth between the external teeth 23 of the external gear 21 and the internal teeth 13 of the internal teeth oscillating bodies 12A and 12B is set to be slight (for example, in a range of about 1 to 4).
The gear system operates in the following manner.
Rotation of the input shaft 5 is delivered to the eccentric shaft gears 7 through the pinion 6. The eccentric shafts 10 are then rotated by the eccentric shaft gears 7. The eccentric bodies 10A and 10B rotate due to rotation of the eccentric shafts 10, then, the internal teeth oscillating bodies 12A and 12B oscillatingly rotate due to the rotation of the eccentric bodies 10A and 10B. Since rotation of the internal teeth oscillating bodies 12A and 12B is restricted, through one rotation of the oscillating rotation of the internal teeth oscillating bodies 12A and 12B, a phase of the external gear 21 which meshes with the internal teeth oscillating bodies 12A and 12B is shifted by the difference in the number of teeth. Thus, a rotation component equivalent to the phase difference becomes the (reduction) rotation of the external gear 21, and reduced rotation is delivered from the output shaft 20.
However, with this variety of internal teeth oscillating-type inner gearing planetary gear system, eccentric shafts for oscillating internal teeth oscillating bodies do not necessarily need to be located at equal intervals circumferentially, nor do all eccentric shafts need to be directly driven. A portion thereof may be driven by following rotation of another component. FIG. 6 shows an example of a construction in which a non-driven eccentric shaft 50A is included and in which each of eccentric shafts 50A through 50C are located circumferentially at non-equal intervals. As another example, a construction is shown in FIG. 7 in which an internal teeth oscillating body 62 is oscillatingly driven by only two eccentric shafts 60A and 60B. These examples are disclosed in Japanese Patent Laid-Open Publication No. 2000-65158.
However, with the gear system disclosed in the former patent publication, because of the three eccentric shaft gears i being located circumferentially at equal intervals are driven by the single (pinion 6 of the) input shaft 5, the input shaft is located coaxially with the output shaft, and thus there was difficulty in creating a design having a hollow shaft passing through the entire gear system. For example, for use as a gear system for joint drives in industrial robots, as a gear system for driving precision machinery, etc., there is often a desire to pass wire harnesses, cooling water piping, etc. through a gear system to a partnered apparatus (driven machine). In such an instance, it meant that designing a driving source such as a motor connected to the input shaft a through-hole was also necessary to design an input shaft with a through-hole. In effect it was nearly impossible to form a large hollow shaft. Further, even if a hollow shaft were to be adopted, a space would be formed inside an input shaft rotating at high speed. It would thus be necessary to install protective piping which would be held so as not to rotate by separate bearings dispsed between the protective piping itself and the inner circumference of the input shaft in order to locate, for example, wire harnesses and cooling water piping in the space. In this respect as well it would be difficult to secure a large enough space, and there would also be cost increases.
In regard to this matter, if a structure is adopted wherein eccentric shafts are located at non-equal intervals in the circumferential direction as described in the latter patent publication, a larger diameter hollow shaft can be formed since an input shaft does not necessarily need to be located coaxially with an output shaft. However, when internal teeth oscillating bodies are driven by a structure wherein the eccentric shafts are located circumferentially at non-equal intervals, a practical problem was encountered in that it was difficult to smoothly oscillate the internal teeth oscillating bodies in a well-balanced manner around the external gear in devices manufactured through a normal manufacturing process. It was therefore necessary to process and assemble each member with especially high precision.